1. Field of the Invention
One embodiment of the present invention relates to an evaluation method of an oxide material, and for example relates to an evaluation method of oxygen behavior in a structure body in which oxide films are stacked.
2. Description of the Related Art
A technique by which transistors are formed using semiconductor thin films formed over a substrate having an insulating surface has been attracting attention. Such transistors are applied to a wide range of electronic devices such as an integrated circuit (IC) or an image display device (display device). As materials of semiconductor thin films applicable to the transistors, silicon-based semiconductor materials have been widely used, but oxide semiconductors have been attracting attention as alternative materials.
For example, disclosed is a transistor whose active layer is formed using an amorphous oxide containing indium (In), gallium (Ga), and zinc (Zn) and having an electron carrier concentration of less than 1018/cm3 (see Patent Document 1).
A transistor including an oxide semiconductor is known to have a problem of low reliability because of high possibility of fluctuation in electrical characteristics, although the transistor including an oxide semiconductor can operate at higher speed than a transistor including amorphous silicon and can be manufactured more easily than a transistor including polycrystalline silicon. For example, the threshold voltage of the transistor fluctuates between before and after a bias-temperature test (BT test).
[REFERENCE]
    [Patent Document 1] Japanese Published Patent Application No. 2006-165528